A new kinetic model for the formation of fibrin gel has been proposed which invokes the formation of a soluble complex of fibrinogen and fibrin as an intermediate. Chromatographic studies of fibrinogen/fibrin solutions at various degrees of progress toward gelation reveal the formation of a soluble species of the appropriate molecular weight. The rate and/or event of fibrin gelation has been found to be strongly affected by the type and amount of added "inert" macromolecules. The ability of proteins to regain native structure and/or enzymatic activity after exposure to elevated heat or high ethanol concentrations has been found to be strongly dependent upon the type and amount of added "inert" macromolecules. Key words: fibrin gelation, gel chromatography, kinetic model, protein stability.